硬膜外脊髓电刺激电压及频率变化对正常大鼠脊髓反射的影响

Effects of epidural spinal cord electrical stimulation with varying voltage and frequency on spinal cord reflexes

目的研究正常大鼠麻醉状态下S1脊髓节段不同电压及频率硬膜外脊髓电刺激（ESCES）所诱发的脊髓反射，探讨ESCES诱发脊髓反射的发生机制及来源。方法选取成年雌性Sprague—Dawley大鼠10只，麻醉后手术将电极植入S1脊髓节段，予以波宽200μs、电压强度分别为400，600，1200mV的单脉冲ESCES；1200mV时，频率分别为50，60，80，100Hz的ESCES。以同心圆针电极记录大鼠后肢半腱肌肌腹的肌电信号，观察所诱导脊髓反射的特点。结果能引起大鼠半腱肌反应的阈值为300mV。3种电压强度的ESCES能诱导出2种潜伏期成分的脊髓反射，较低的400，600mV电压强度可诱发出长潜伏期成分，潜伏期分别为（5．27±0．36）ms和（5．19±0．67）ms；较高的1200mV电压强度可诱发出短潜伏期成分，潜伏期为（2．57±0．23）ms。4种较高频刺激均可诱发出脊髓反射，但刺激后期都出现了脊髓反射脱落后不规律出现，部分大鼠出现了较高频刺激后期脊髓反射完全消失。50Hz频率的ESCES所诱发脊髓反射的潜伏期和波宽分别为（4．46±1．07）ms和（7．33±1．00）ms，与另外3种频率所诱发脊髓反射相比差异有统计学意义（P〈0．05）。结论不同电压的ESCES可诱导出不同来源的脊髓反射。长潜伏期成分可能是兴奋脊髓背根传入神经后引起的单突触反射；短潜伏期成分可能是直接兴奋脊髓内的运动神经元或运动纤维后向下传导引起的肌肉兴奋电反应。4种较高频ESCES所诱发的不规律出现的脊髓反射，可能是一种单突触反射。较高频刺激时脊髓反射的不规律出现可能与较高频刺激的抑制作用有关。

Objective To investigate the effects of epidural spinal cord electrical stimulation （ESCES） on spinal cord reflexes in normal adult rats, and to find out where and how the spinal cord reflexes are generated. Methods Ten adult female Sprague Dawley rats were anaesthetized and an electrode was placed at the S1 spinal cord segment. Single electric pulses with 200 μs pulse width and voltages of 400 mV, 600 mV and 1200 mV were used in the ESCES. 1200 mV voltages with 50 Hz, 60 Hz, 80 Hz, 100 Hz frequency were also tested. EMG signals were recorded with concentric needle electrodes in the rats＇ semitendinosus muscles to observe the characteristics of spinal cord reflexes. Results The voltage threshold for generating semitendinosus muscle response was 300 mV. The three ESCES voltages induced 2 kinds of spinal cord reflexes. The 400 mV and 600 mV stimulation induced spinal cord reflexes with short latency （5.27 ± 0.36 ms and 5.19 ± 0. 67 ms respectively）. The 1200 mV stimulation volt- age induced spinal cord reflexes with long latency （2.57 ± 0. 23 ms）. Spinal cord reflexes could be generated by 50 Hz, 60 Hz, 80 Hz, and 100 Hz ESCES. At the higher frequencies, spinal cord reflexes declined late in the ex- periments and then appeared irregular. In some of the rats, spinal cord reflexes vanished entirely late in the stimulation experiments. The latency and duration of the spinal cord reflexes induced by 50 Hz ESCES were （4.46 ± 1.07） ms and （7.33 ± 1.00）ms respeetively. These were significantly different from the latency and duration initiated by 60 Hz, 80 Hz or 100 Hz ESCES. Conclusions Different ESCES voltages induce different spinal cord refle- xes generated differently. The long latency reflexes might be monosynaptic responses mediated by dorsal root excitement, while the short latency reflexes might be sarcous exciting electric activity mediated by direct excitement of motor neurons or motor fibers. The irregular spinal cord reflexes induced by higher frequency ESCES might be one kind of monosynaptic response, hregularly appearing spinal cord reflexes induced by higher frequency stimulation might due to the inhibitory effect of higher frequency stimulation.